This invention relates generally to electric shift apparatus especially suited for use with a motor vehicle having an automatic transmission and more particularly to a control system for such an electric shift apparatus.
Motor vehicles since their inception have required some manner of gear change mechanism to satisfy the varying torque and speed requirements encountered during the typical duty cycle of a motor vehicle. For many years these gear change mechanisms were manual in the sense that they required an operator input from a shift lever or the like to effect each desired gear change ratio. More recently, so called "automatic" transmissions have become popular in which much of the shifting is done without operator input in response to speed and throttle opening parameters. These automatic transmissions typically include a mode select member on the transmission housing movable between a plurality of selected positions corresponding to a respective plurality of shift modes within the transmission. The mode select member is moved between its several shift positions via a cable or linkage mechanism extending from the mode select member to a suitable gear selector lever located in the passenger compartment of the vehicle.
More recently, control systems have been developed for motor vehicle automatic transmissions wherein electrical signals are generated by a suitable action on the part of the driver and transmitted electrically to some manner of power means arranged to move the mode select member. Examples of such control systems are shown for example in U.S. Pat. Nos. 4,790,204, 4,817,471, 4,841,793 and 4,843,901, all assigned to the assignee of the present application. Whereas the control systems of these patents have proven to be generally satisfactory, it is important that the control system operate in a manner to move the mode select member rapidly between its various positions and yet ensure that each position is arrived at cleanly, positively, and without overshoot.